The present invention relates to an electronic guidance system and method for accurately locating a boring device, and more particularly to a wireless guidance system and method wherein the use of two guidance techniques minimizes the error in locating the boring device.
Directional drilling refers to a type of drilling where a drill tool is directed along a predetermined path by an operator located at a boring machine. By guiding the drill tool from the drilling site, cabling, pipes, or other underground conduits may be installed with minimal disruption to the surface above the location where the borehole is being drilled. Directional drilling techniques have therefore become especially prevalent where there are obstacles on the surface that would make trenching or other conventional installation techniques impossible. For example, directional drilling techniques are especially advantageous when constructing a horizontal borehole beneath a body of water, a roadway, or buildings. Because directional drilling can proceed without regard to surface structures, it has become the chosen technique for many applications.
One direction drilling technique incorporates two guidance packages located within a drill tool. The primary guidance package comprises a triaxial magnetometer and triaxial accelerometer. The set of signals produced by the triaxial magnetometer and triaxial accelerometer are transmitted via a cable to a guidance computer and manipulated to determine the orientation of the drill tool and, by integration over the distance the drill tool has traveled, the approximate position of the drill tool during the directional drilling operation. The secondary guidance package comprises a magnetic solenoid transmitter that is placed within the drill tool. The magnetic solenoid transmitter emits an electromagnetic field having a predetermined radiation pattern. Using a locating device such as the device disclosed in U.S. Pat. No. 4,806,869 to Chau et al. (expressly incorporated herein by reference), an independent indication of the position of the drill tool can be determined. When used in conjunction, the two guidance packages ensure accurate guidance of the drill tool.
In operation, the magnetometer and accelerometer are used to guide the drill tool during the boring operation. However, the actual position of the drill tool is determined using the locating device. When the actual position is determined, errors which have crept into the calculated tool location may be removed by updating the calculated position of the drill tool to equal the actual drill tool position. By eliminating the integration error, the predetermined boring path may be more accurately followed.
Although the use of this system may provide a more accurate means for locating a boring device, it has a significant drawback in that a cable is required to transmit the data from the primary navigation package. The use of this cable has several disadvantages. As a drilling run proceeds, drill rods must be added to create a drill string. Each time a drill rod is added to the drill string, the wire must be extended to accommodate the increased length of the drill string. Extending this wire is time-consuming, thereby greatly reducing productivity.
A second disadvantage of using a cable is that it may fail or short to a drill rod. This greatly reduced the reliability of the guidance system, and should a failure of this type occur, substantial time may be required to correct the fault.
A third disadvantage of the use of a cable to transmit data from the primary navigation system is that a drill operator""s safety may be in jeopardy. The act of extending the cable each time that a drill rod is added to a drill string requires the operator to be in close proximity to the drill machinery for a longer period of time; therefore, this reduces the margin of safety for the operator.
Attempts to eliminate the cable connection for transmitting navigational data have had little success. One such method transmits data through a circuit made up of the drill pipe with the return electrical path being the earth. This unit is powered by an internal battery pack. A problem with this method is that it has a very limited range, which in turn limits the maximum length of a drilling run.
Another method of wireless guidance of a boring device is called mud pressure pulsation. Currently, its use is impractical for medium to small drilling rigs due to its large size and high cost. These systems are typically used with oil drilling rigs. Wireless guidance systems that transmit navigational data from magnetometers and gravity vector sensors exist, but the current level of development makes their use impractical because of their limited range.
There exists a need for a wireless guidance system that can be used to accurately guide a drilling device along a predetermined drilling path. The system needs to have a long enough range, yet be small and cost-effective so as to be practical for use for medium to small range drilling rigs.
In accordance with one embodiment of the invention, a wireless electronic guidance system for accurately locating an in-ground boring device is provided. The system includes a primary guidance package for indicating the position of the boring device and a secondary guidance package for indicating the position of the boring device. The secondary guidance package includes a magnetic solenoid transmitter for both transmitting data from the primary guidance package and emitting a signal from the secondary guidance package to a data receiver for receiving the guidance data. The primary guidance package and secondary guidance package are all coupled to the boring device. The magnetic solenoid transmitter has the capability of transmitting the data from the primary guidance package and the secondary guidance package a distance of at least 100 feet. The data receiver is typically mounted above ground and near the drill operator.
In an embodiment of the invention, the primary guidance package contains accelerometers and magnetometers. The signals from the primary guidance package are used to calculate pitch and roll orientation from the gravity vector sensor, and orientation to the magnetic north pole from the magnetometers. This data is then transmitted via the magnetic solenoid transmitter to the data receiver for calculation of the location of the boring device.
In another embodiment of the present invention, the secondary guidance package containing the magnetic solenoid transmitter generates an electromagnetic field having a predetermined radiation pattern. A locator that locates the electromagnetic field is positioned above ground. The locator detects the electromagnetic field transmitted from the magnetic solenoid transmitter and determines the actual position of the boring device.
In still another embodiment of the invention, the magnetic solenoid transmitter is of a length such that the magnetic flux density of the signal emitted from the magnetic solenoid transmitter is sufficient to be received by the data receiver at distances of at least 100 feet. Contrary to what was known by someone skilled in the art, as the length of this magnetic solenoid transmitter increases, the flux density of the emitted signal increases. In an embodiment of the invention, the length of the magnetic solenoid transmitter is at least eight inches.
In yet another embodiment of the invention, the wireless transmitter is a magnetic solenoid transmitter having at least two magnetic solenoid transmitters co-axially aligned and operating as one single, in-phase magnetic solenoid transmitter. Typically, the transmitter will have two coaxially aligned magnetic solenoid transmitters of length of at least eight inches to provide transmission of data from both the primary guidance package and secondary guidance package to the data receiver over distances of at least 100 feet.
In a further embodiment of the invention, a method is provided for accurately guiding an in-ground boring device along a predetermined bore hole path by monitoring its location along the path. The boring device contains both a primary guidance package and a secondary guidance package. The method includes receiving the data from the primary guidance package from a magnetic solenoid transmitter having a length of at least eight inches, calculating the position of the boring device, guiding the boring device along the predetermined path based on that calculated position, receiving data from the secondary guidance package from the magnetic solenoid transmitter having a length of at least eight inches, calculating a second position of the boring device, and setting the position calculated based on data from the primary guidance system equal to the position based on data gathered from the secondary guidance system to remove any error present in the first calculated position.
In still a further embodiment of the invention, a longer magnetic solenoid transmitter is incorporated with current drilling techniques to increase the length of transmission of guidance or location data. The current drilling techniques can benefit from and increase in field strength with out an accompanying increase in required power.
In yet another embodiment of the invention, a magnetic solenoid transmitter comprising at least two magnetic solenoid transmitters co-axially aligned to operate as a single, in phase transmitter is incorporated with current drilling techniques to increase the length of transmission of guidance or location data. The current drilling techniques can benefit from and increase in field strength without an accompanying increase in required power.
The present invention has many advantages. The elimination of any wire or cable connection to a data receiving computer addresses the long-unsolved problem of having to extend the length of the wire or cable connection as the length of the drill string increases, worrying about the wire or cable shorting against the inside of a drill rod or becoming disconnected, and placing the operator in a position of potential danger. The invention is also a simplified guidance system by transmitting both the primary guidance package data and the secondary guidance package data over a single transmitter. Furthermore, the need to correct the calculated position based on data from the primary navigational package is reduced; thus, the system operates more efficiently and economically than other wireless systems. This advantage also permits guidance of the boring device with greater accuracy due to the long range transmitting capability of the transmitter in areas where location of the boring device using the secondary guidance package is unfeasible.